As a representative example of a wireless power transmission system, a magnetic-field-coupling-method power transmission system is known in which power is transmitted by utilizing a magnetic field from a primary coil of a power transmission device to a secondary coil of a power reception device. In this system, when power is transmitted by magnetic field coupling, the magnitude of the magnetic flux passing through each coil greatly affects the electromotive force and therefore high accuracy is necessary in the relative positional relationship between the primary coil and the secondary coil. In addition, coils are utilized and therefore it difficult to reduce the size of the devices.
In contrast, an electric-field-coupling-method wireless power transmission system is also known as disclosed in Patent Documents 1 and 2. In such a system, power is transmitted via an electric field from a coupling electrode of a power transmission device to a coupling electrode of a power reception device. In this method, the degree of relative positional accuracy for the coupling electrodes is comparatively low and it is possible to reduce the size and the thickness of the coupling electrodes.
Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2009-531009.
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2009-296857.
An example of a power reception device in a wireless power transmission system is an electronic appliance such as a cellular phone device, a laptop PC or a tablet terminal. For example, the wireless power transmission system is used to wirelessly charge secondary batteries of these electronic appliances. When the power reception device is for example a tablet terminal in which the secondary battery has a large charging capacity, there is a problem that the charging time is long when power transmission is not efficiently performed.